1. Field of the Invention
This invention relates generally to a needle thread supply device, in a two needle sewing machine with a single needle pause function, and more particularly to such a needle thread supply device which uses a needle thread control technique.
2. Prior Art
A sewing machine having two needles arranged in parallel with each other, and a mechanism for temporarily holding one of the needles in an inoperative condition, has heretofore been known as disclosed in U.S. Pat. No. 3,545,390. Such an apparatus may, of course, be used for sewing together two fabrics. For example, with reference to FIG. 5 of the instant application (which illustrates a stitching pattern) when two fabrics a1, a2 are placed one over the other and such a prior device is used to form two parallel seams Ti, To, only one needle (i.e., the needle located at the outside of the corner of the fabrics laid one over another) sews a seam To1-To2 (in the shaded area in FIG. 5) in seaming an angular portion. Meanwhile, the other needle (i.e., the needle located at the inside of the corner of the fabrics) is maintained in a pause condition.
When the needle located at the inside of the corner is unoperated, the thread which is inserted in the entry of the needle is not consumed as the seam is not formed thereby. However, in the sewing machine of the above type, provided that one of the needles, that is, the needle inside of the corner is paused, the paused needle thread is caught between the fabrics and the pressor foot and is then pulled out of the needle inside of the corner simultaneously with movement of the fabrics.
It is apparent from the foregoing that the needle thread is inevitably drawn from the thread tension unit when the seam To1-To2 outside of the corner is made to a considerable extent.
As a result, a disadvantage derived from such a conventional mechanism is that when the needle which has been paused is re-operated to form a seam starting from an apex (stitch) Ti, the needle thread drawn from the thread tension unit is not subjected to thread tension, thereby having the needle thread bulged out of the back of the fabrics or raised from the fabrics.